Purpose:
There is sufficient evidence to suggest that visual acuity does not correlate with macular thickness in patients with diabetic macular edema (DME). It is unclear whether other visual function tests would correlate with the central subfield thickness (CSF) as measured by spectral domain optical coherent topography. In this study, we assessed the correlation of various visual function tests in DME with CSF

Methods:
This is a prospective study on 22 eyes of diabetic patients with centre-involving macular edema. Best corrected visual acuity (BCVA), contrast sensitivity (Pelli Robson letter score) and foveal and retinal sensitivity measured by microperimetry (Nidek MP1) were recorded. Maximum reading speed (MRS) was evaluated using MNRead acuity charts. The central subfield thickness (CST) was performed using a standard protocol on the Heidelberg Spectralis SD-OCT. The Pearson correlation coefficient (r) was used to measure the linear association between visual function test score and between these scores and OCT-measured CST. P < 0.05 was considered statistically significant.

Results:
The correlation coefficient for the association between CSF and BCVA was -0.273 (p=0.219), contrast sensitivity was 0.095 ( p-value 0.673), MRS was 0.344 (p-value 0.116), foveal sensitivity was -0.365 (p-value 0.095) and retinal sensitivity was -0.271 (p-value 0.223). On the basis of multivariate regression models, none of these visual function parameters were significantly associated (P<0.05, after adjusting for multiple testing) with CST.

Conclusions:
In DME, the combination of MRS, retinal senstivitiy and visual acuity score is advocated to provide a more comprehensive assessment of retinal function. However, none of these tests correlated with CST suggesting that CST is not an appropriate measure to assess structure-function correlation in DME.